The present invention relates to an electric switch whose fixed contacts incude printed conductors on a printed circuit board which are coated with a layer of noble metal, and whose moving contacts are designed as sliding contacts capable of moving along predetermined contact paths over the fixed contacts on the printed circuit board, and in which on one contact path there are provided several fixed contacts which are electrically connected to each other.
Various types of electric switches are known in the art in which the fixed contacts are formed by parts of printed conductors disposed on a printed circuit board. The moving contacts of such switches are designed as sliding contacts, either as contact springs or as contact members which, with the aid of springs separated therefrom are pressed on to the contacts on the printed conductor. The sliding contacts are guided along predtermined paths over the fixed contacts on the printed circuit board, that is, in the case of rotary switches along circular paths and, in the case of sliding switches, on straight paths.
As the material for the printed conductors there is mostly used a layer of copper laminated on to the printed circuit board and from which the printed conductors, preferably by employing a photoetching process, are etched out. The printed copper conductors, however, are unsuitable for use as contacts in a switch, because the copper easily oxidizes thus increasing the transfer resistance between the moving and the fixed contacts to an inadmissible extent.
Therefore, such fixed contacts which are formed by printed conductors, are coated as a rule, with a layer of noble metal, such as with a layer of gold. This gold plating is mostly deposited in the course of a galvanic process. In the course of this, all printed conductors of the printed circuit board are coated with a layer of gold.
Although the gold plating has a very small thickness, less than millimeter, the gold layer which is indispensable for the stationary contacts, runs up to a considerable portion of the price for the entire printed circuit board.
One has therefore proceeded to provide only those parts of the printed conductors of the printed circuit board with a gold plating which actually serve the contact making. This is done in such a way that a pattern of lacquer is printed on, which only covers up those parts of the printed conductors which are not supposed to be provided with a gold plating. In this way it is possible to save a considerable amount of the costs for the layer of gold.
After the gold-plating of the free sections of the printed conductors, the covering lacquer remains on the printed circuit board, because a removal would involve additional processing steps and costs, and because it simultaneously also serves as a corrosion protection for those part of the printed conductos which are not coated with a layer of noble metal.
The covering lacquer for the gold plating, however, may in no case be applied to those parts of the printed circuit boards which correspond to the contact paths of the moving contacts. Owing the wear during actuation of the switch, the material of the layer of lacquer would get on to both the moving an the fixed contacts and would thus result in considerable contact disturbances. It has therefore been accepted that within the area of the contact paths of the moving contacts a covering of the printed conductors prior to the gold plating is impossible.
In these prior art switches, several fixed contacts disposed on one contact path are electrically connected to each other. One example of such switches are the so-called code switches. Up to now, such fixed contacts which are electrically connected to one another and disposed on one common contact path, have been designed as one single continuous contact which, of course, has to be provided throughtout its entire length with a coating of noble metal, such as a layer of gold.
It is the object of the invention to achieve a further saving of noble metal in the case of switches of the aforementioned type.